1. Field of the Invention
The present invention relates to a coil apparatus for use as a transformer or a choke coil, for example, and to a method for manufacturing the coil apparatus.
2. Description of the Related Art
FIG. 5A is an exploded view of a conventional of a coil apparatus; FIG. 5B is a sectional view of the coil apparatus shown in FIG. 5A at the line Axe2x80x94A. A coil apparatus 1 shown in FIGS. 5A and 5B comprises a substrate 2 for mounting electronic components thereon, a coil pattern 3 formed on the substrate 2, a core 4 comprised of a pair of core members 4a and 4b, and a core-combining member 5.
The substrate 2 having electronic components and a circuit pattern mounted thereon, which form a circuit, is preferably a multilayer substrate formed by joining plural substrates together. For example, the plural substrates which form the substrate 2 may respectively have coil patterns 7 coaxially formed about an axis defined on the substrate 2. The coil pattern 3 is formed by connecting a plurality of the coil patterns 7. In addition, when the coil apparatus 1 is to be a transformer apparatus, at least one of the plural coil patterns 7 forms a primary coil and the remaining coil patterns 7 form one or more secondary coils.
In the example shown in FIGS. 5A and 5B, the core members 4a and 4b are molded by pressing and sintering magnetic powder such as ferrite, and are E-shaped in cross-section, each having a planar bar portion 8 and core legs 9a, 9b, and 9c arranged to respectively extend from one end, the center, and the other end of the bar portion 8.
The substrate 2 is provided with through-holes 10a, 10b, and 10c for receiving the core legs 9a, 9b, and 9c, respectively. The through-hole 10b is formed within the coil pattern 3. Into these through-holes 10a, 10b, and 10c, as shown in FIG. 5B, the core legs 9a, 9b, and 9c of the core members 4a and 4b are respectively inserted from top and bottom surfaces of the substrate 2, so that the core legs 9a, 9b, and 9c of the core member 4a on the top side respectively abut the core legs 9a, 9b, and 9c of the core member 4b on the bottom side.
The core-combining member 5, as is shown in FIG. 5B, is disposed surrounding the pair of core members 4a and 4b and elastically holds them together. The core-combining member 5 is made by bending a metallic plate so as to form a web 12, leg portions 13a and 13b, and claw portions 14a and 14b. That is, the two sides of the web 12 covering the bar portion 8 of the core member 4a are respectively bent in the direction along the core legs 9a and 9c of the core members 4a and 4b so as to form the leg portions 13a and 13b; and the ends of the leg portions 13a and 13b are further bent inwardly so as to form the claw portions 14a and 14b. 
The space between the web 12 and the claw portions 14a and 14b, as is shown in FIG. 5B, is approximately the same as the distance h from the top surface 8a of the bar portion 8 of the core member 4a to the top surface 8a of the bar portion 8 of the core member 4b when the core legs 9 of the core member 4a on the top side are abutted with the core legs 9 of the core member 4b on the bottom side. As is shown in FIG. 5B, the web 12 and the claw portions 14a and 14b clamp the bilateral sides of the core members 4a and 4b in the abutment state from both sides and from the top and bottom sides. Thereby, the core members 4a and 4b are combined together so as to be relatively movable in the direction xcex1 (front-and-rear) indicated in FIG. 5A. The through-holes 10a, 10b, and 10c have the length W in the front-to-rear direction, along which the core members 4a and 4b can move in the front-to-rear direction as mentioned above.
The coil apparatus 1 shown in FIGS. 5A and 5B is assembled as follows: First, the core member 4a is arranged above the substrate 2 on which the coil pattern section 3 and the through-holes 10a, 10b, and 10c are formed while the core member 4b is arranged below the substrate 2. The core legs 9a, 9b, and 9c of the top core member 4a are inserted into corresponding through-holes 10a, 10b, and 10c from the top of the substrate 2 while similarly, the core legs 9a, 9b, and 9c of the bottom core member 4b are inserted into the corresponding through-holes 10a, 10b, and 10c from the bottom of the substrate 2. Thus, the core legs 9a, 9b, and 9c of the top core member 4a are abutted against the core legs 9a, 9b, and 9c of the bottom core member 4b, respectively.
From the upper side of the core members 4a and 4b in the abutment state, the left leg portion 13a of the core-combining member 5 is inserted into the left through-hole 10a while the right leg portion 13b of the core-combining member 5 is inserted into the right through-hole 10c, the through-holes 10a and 10c respectively corresponding to the outward core legs 9a and 9c of the core members 4a and 4b. 
Thereby, the core members 4a and 4b in the abutment state and the core-combining member 5 are fitted with each other so that the core members 4a and 4b are assembled to the substrate 2 by being combined with the core-combining member 5. In such a manner, by being assembled to the substrate 2, the core members 4a and 4b sandwich a part of the coil pattern section 3 therebetween from the top and bottom sides of the substrate 2.
Then, the combined core members 4a and 4b are relatively slid in the front-to-rear direction, so that the abutment portions between the core members 4a and 4b, namely the ends of the core legs 9a, 9b, and 9c which are abutted with each other, are rubbed together. By rubbing the ends of the core legs 9a, 9b, and 9c together, the following advantages can be obtained.
Since as described above the core members 4a and 4b are molded by sintering magnetic powder, the end faces of the core legs 9a, 9b, and 9c of the core members 4a and 4b are rough, and also dust may get in between the end faces of the core legs 9a, 9b, and 9c which are abutted to each other when combining the core members 4a and 4b together. Thus, adhesion between the end faces of the core legs 9a, 9b, and 9c which are abutted to each other may be low. But by rubbing the end faces of the core legs 9a, 9b, and 9c against each other by rubbing the cores together as mentioned above, the end faces of the core legs 9a, 9b, and 9c are polished to have substantially a mirror finish, while dust which has gotten in between the end faces of the core legs 9a, 9b, and 9c is crushed and removed, thereby improving the contact between the end faces of the core legs 9a, 9b, and 9c of the top core member 4a and the end faces of the core legs 9a, 9b, and 9c of the bottom core member 4b. By contacting the core members 4a and 4b together in such a manner, inductance can be improved, thereby improving the performance of the coil apparatus.
However, in the conventional structure, as is shown in FIG. 5B, internal faces 8b of the bar portion 8 of the core member 4a are necessarily brought into contact with a surface of the substrate 2. Therefore, the surface of the substrate 2 is rubbed by the internal faces 8b of the bar portion 8 when rubbing the cores together, which may cause a protecting member such as a resist formed on the surface of the substrate 2 to be damaged or to be peeled off. Such damage to the protecting member may cause a problem, in that a circuit pattern such as copper formed on the substrate 2 may corrode or its withstand-voltage performance may be reduced when the coil apparatus is placed under high-humidity circumstances for a long time.
The present invention solves the above-described problem and provides a coil apparatus and a method of manufacturing the coil apparatus, which is capable of avoiding damage to a protecting member formed on a surface of a substrate for mounting electronic components due to the movement of core members when the core members are rubbed together during the assembly of the coil apparatus, so as to improve reliability.
In order to achieve this, the present invention provides several structures which solve the above-described problems. For example, a coil apparatus according to a first aspect of the present invention comprises a substrate for mounting electronic components; a coil pattern formed on the substrate; a pair of core members mounted on the coil pattern so as to sandwich a part of the coil pattern therebetween from the top and bottom sides of the substrate, at least one of the pair of core members having core legs; through-holes for receiving the core legs formed in a portion of the substrate at the center of the coil pattern and in a portion of the substrate outside the coil pattern; a core-combining member for holding the pair of core members together, so that the core members are movable with respect to each other in front and rear directions, by clamping both the core member on the top-face side of the substrate and the core member on the bottom-face side of the substrate from the top and bottom sides of the substrate via the through-holes; and a cover member arranged to be fixed to the substrate, wherein the cover member has surfaces which raise and hold the core-combining member so as to separate both core members from the substrate resulting in a non-contact state, by forming a space between opposing faces of the substrate and the core members held by the core-combining member.
In a coil apparatus according to another aspect of the invention, the core-combining member may be provided with leg portions which are inserted into the through-holes on the outside, to the right and the left, of the right and left core legs, each leg portion having an inclined face formed on an external side thereof, the inclined face being inclined outwardly so as to become more distant from the core members as the inclined face proceeds from the bottom face toward the top face of the substrate; and also, the cover member may be provided with leg portions which are inserted into the same through-holes at positions outside the leg portions of the core-combining member, the leg portions of the cover member each having an inclined portion formed thereon, the inclined portions being inclined in a direction to raise the core-combining member by abutting against the inclined faces of the leg portions of the core-combining member.
A method for manufacturing a coil apparatus according to a second aspect of the present invention comprises the steps of: arranging the pair of core members, one core member on the top face of the substrate for mounting electronic components, the other on the bottom face of the substrate; securing the pair of core members together with the core-combining member so as to mount the core members on a coil pattern of the substrate; raising and holding the core-combining member with the cover member so that the cover member is fixed to the substrate and the core members are separated from the substrate for mounting electronic components resulting in a non-contact state therebetween; and sliding the core member on the top side of the substrate relative to the core member on the bottom side thereof so as to rub a contacting portion between the core member on the top side and the core member on the bottom side so that the contacting portions between the core member on the top side and the core member on the bottom side are brought into full contact.
In the structures according to the present invention, the core-combining member holding the core members together is raised and held by the cover member so as to form a clearance between opposing faces of the core member and the substrate for mounting electronic components, resulting in a non-contact state between the core member and the substrate.
Accordingly, when the cores are rubbed against each other during the assembly of the coil apparatus, the surface of the substrate for mounting electronic components can be protected from being damaged by the sliding core members. Thereby, damage to the protecting member on the top surface of the substrate due to the rubbing can be prevented so as to avoid problems such as corrosion of a circuit pattern on the substrate and withstand-voltage performance degradation. Therefore, a highly reliable coil apparatus can be provided.
The right, left, front, and rear directions mentioned in this specification are the directions which exist when the substrate for mounting electronic components is horizontally placed; however, the position of the substrate is not limited to be horizontal, and the right, left, front, and rear directions above may be different from those when actually viewing.
Other features and advantages of the present invention will become apparent from the following description of embodiments of the invention which refers to the accompanying drawings, in which like references denote like elements and parts.